The present invention relates to a method and an apparatus for separating solid particles from flue gases in a circulating fluidized bed reactor, in which method the flue gases are led to a cyclone separator in which the separated solid particles are discharged and returned to the reactor.
The object of the invention is to provide a device by means of which the solid particles can be not only separated effectively from the flue gases, but also separated into coarse and fine particles which are returned separately to the reactor.
The circulating fluidized bed technique has long been applied, e.g., in calcinators, and is now often utilized in various reactors, such as combustion chambers and gasifiers. In known applications, the separation of solid particles from flue gases takes place in the lower part of a funnel-shaped cyclone separator, and, specifically, in the cylindrical vortex chamber of the separator, in which is disposed a gas outlet pipe that leads the flue gases upwards, and from which the solid particles are returned to the reactor via a discharge pipe.
A strong underpressure and a high axial flow speed are, as known, formed in the center of conventional cyclone separators. Due to this, an ordinary cyclone tends to create suction in the discharge pipe. The resulting suction flow does not usually have a tangential speed and consequently all particles transported with it are led out via the central pipe of the cyclone.
The solid material discharged with gas from the separator is mainly fly ash containing particles smaller than 100 .mu.m, which is later separated by means of electro- or tube filters. Fly ash contains considerable amounts of unburnt particles and lime that has not had time to react with SO.sub.2 in the reactor. In addition, the separation degree of a cyclone separator decreases with the growth of the size of the cyclone.
In the method according to this invention, a considerable part of the flue gas particles smaller than 100 .mu.m can be separated from the coarser particles and returned to the reactor.
The method according to this invention is characterized in that solid particles are discharged from a cyclone separator by means of suction.
The apparatus according to the invention is characterized in that between the lower part of the funnel-shaped cyclone separator and the return duct for the larger solid particles there is disposed a suction chamber for separating and removing the finer particles.